Using \bigl and \bigr in the first formula makes the parentheses slightly bigger, which is good for reading in this case. Since they are almost necessary in the furst summation, I used them also in the second one, for symmetry.

The align environment is for multiline displays; if you want the equation numbered, then use equation instead of equation*.

But in any case, the contents of equation, align and similar environments is already assumed to be math, so adding $ will give errors.